A massive cave discovered in a remote region of Vietnam has been explored for the first time, and is now believed to be amongst the largest in the world. With its main chamber stretching nearly 500 feet in length, and soaring to an unbelievable 650 feet in height.

The cavern is called Hang Son Doong, which means “mountain river cave” in Vietnamese, and was first discovered back in 1991, but was not explored until recently, when a 13-man spelunking team from the U.K. went inside for the first time. The team used a high tech laser to plumb the length and depth of the cavern, and based on preliminary results, they now believe that the cave reaches a height that is at least twice as tall as the largest previously known cave.

The expedition trekked six hours through the jungle to reach the cavern, then spent five days exploring it. In order to reach the massive main chamber. they had to rappel down into a side chamber, cross two underground rivers, and then negotiate several passages. Their cursory survey revealed that the cave system is more than 4 miles in length, but the team believes that there is much more yet to be discovered, and they’ll return later in the year to more thoroughly investigate its depths.

While this cave is genuinely an amazing find, and the height of its main chamber may be the largest yet discovered, it pales in comparison to a cave called Gua Nasib Bagus in Malayasia, whose main chamber streches 2300 feet in length. The king of caves remains Mammoth Cave system in Kentucky however, as it streches at least 365 miles in length, with more passages being discovered all the time.